Anaerobic gut fungi (AGF, Neocallimastigomycota ) represent a phylum of zoospore-producing fungi inhabiting the gastrointestinal tracts of herbivores. Twenty mammalian-affiliated genera (M-AGF) and two tortoise-affiliated genera (T-AGF) have been described so far. Here, we report on three additional novel T-AGF isolates obtained from Texas tortoises ( Gopherus berlandieri ; GX isolates) and African spurred or sulcata tortoises ( Centrochelys sulcata ; SR and TM isolates). Phylogenetic analysis using the D1-D2 regions of the large ribosomal RNA subunit (D1-D2 LSU), RNA polymerase II large subunit, internal transcribed spacer-1 (ITS-1) region and transcriptomics-enabled phylogenomic analysis clustered these strains into three distinct, deep-branching clades, closely related to previously described T-AGF genus Testudinimyces . All isolates displayed filamentous rhizoidal growth patterns and produced monoflagellated zoospores. Unique morphological characteristics included the production of elongated, thick, nucleated structures in GX isolates, the formation of thin hair-like projections on sporangial walls in SR isolates and irregularly shaped sporangia in TM isolates. All strains grew optimally at 32–35 °C and showed distinct substrate utilization capacity (e.g. growth on pectin, chitin, galactose). LSU analyses revealed GX isolates as the first cultured representatives of tortoise-affiliated but previously uncultured lineage NY56, while SR and TM strains have not been encountered in prior culture-independent AGF surveys. We propose to accommodate these isolates in three new genera and species – Gopheromyces tardescens (GXA2), Gigasporangiomyces pilosus (SR0.6) and Kelyphomyces adhaerens (TM0.3). Furthermore, based on the ecological, physiological and phylogenetic distinctions between T-AGF and M-AGF, we propose to establish a new family ( Testudinimycetaceae ) to accommodate the genera Testudinimyces, Gopheromyces , Gigasporangiomyces and Kelyphomyces .
Morris et al. (Fri,) studied this question.
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